In an angular cap known from U.S. Pat. No. 4,553,955, the vertically inclined holders are in the form of bores distributed about the circumference of the angular cap, and adapters are introduced into the holders. Each test tube containing the material to be centrifuged is inserted into a respective adapter. The provision of the individual bores in particular makes this type of known angular cap very expensive and labor-intensive to manufacture. To hold 24 test tubes, for example, 24 bores must correspondingly be provided at the circumference of the angular cap, which is relatively time consuming and tedious work, because the bores must be made precisely symmetrical to one another to prevent the danger of an out-of-round operation during centrifuging.